The present invention relates to a novel tetrafluoroethylene (hereinafter referred to also as TEE)/ethylene copolymer (hereinafter referred to also as an EFT copolymer), and a film made of such an EFT copolymer excellent in flexibility, dust-proofing property, light transmittance, high strength, non-tackiness, etc. Further, it relates to an agricultural covering material, a release film and an interlayer for laminated glass, made of such a film.
Heretofore, as an agricultural covering material for a tunnel house or a pipe house, a film made of e.g. an ethylene/vinyl acetate copolymer, a polyester resin or a soft vinyl chloride resin, has been used. Especially, a soft vinyl chloride resin film is superior to films of other materials with respect to an application efficiency, price, warmth retaining property, etc. And thus is used mostly as an agricultural covering material. However, the soft vinyl chloride film contains a plasticizer and thus has a difficulty such that the film surface is likely to be soiled by bleeding out of the plasticizer, and the light transmittance tends to deteriorate soon.
Further, many of the above conventional films have an ultraviolet absorber incorporated to improve the weather resistance, but due to deterioration attributable to e.g. sunlight, atmospheric temperature, wind and rains, oxidation, etc., they have to be replaced usually in one to two years. Besides, such films having an ultraviolet absorber incorporated, shield ultraviolet rays inevitably, although there may be a difference in the degree of ultraviolet absorptively. Accordingly, such films are not suitable for cultivation of crop plants which require ultraviolet rays (such as eggplants or certain types of flowers) or for cultivation of crop plants to be pollinated by e.g. bees, Mahana-abu or drone flies which require ultraviolet rays (such as strawberries, melons, water melons or green peppers).
Further, in recent years, really large sized houses have been employed for the purpose of labor saving in house control, enlargement of the cultivation area and prolongation of useful life of houses. For such large sized houses, a covering material made of e.g. a polyester resin, a polycarbonate resin, a soft vinyl chloride resin, an acrylic resin, a fiber reinforced plastic or an inorganic sheet glass, has been used for application for a long period of at least 5 years. However, such a covering material is thick and heavy and has to be applied to a house having a large sized special base material framework, whereby the application work is complex and relatively expensive. Further, a covering material made of a polyester resin, a polycarbonate resin, a hard vinyl chloride resin, an acrylic resin or the like has a drawback that cracks are likely to form by e.g. hail, and the formed cracks are likely to propagate. Further, in the covering material of such a plastic plate contains an ultraviolet absorber in many cases, and thus has the same problem as the above described film containing an ultraviolet absorber.
For the purpose of solving such problems, a film of a fluorine resin is known which is excellent in weather resistance durability and acidic rain resistance and has a long useful life of from 10 to 15 years, and which has excellent characteristics that it is hardly soiled, or a soil can readily be removed by rain water, and it is scarcely breakable. Especially, a film of an EFT copolymer further has excellent characteristics such as heat resistance, weather resistance, light transmittance and non-tackiness and thus is proposed as an agricultural covering material and is partly commercialized.
On the other hand, when a film of an agricultural covering material is stretched over e.g. a pipe house, it is applied by fixing it to the framework of the house by means of a fixing member, while taking care so that the tension of the film will not loosen. However, a conventional film of an ETFE copolymer has a large tensile modulus of elasticity and is poor in flexibility, and there has been a practical problem that the film has to be fixed by a large tensile force.
Further, also in the field of release films to be used for formation of printed boards, a film of an ETFE copolymer is used from the viewpoint of the non-tackiness and heat resistance. Also in this case, conventional ETFE copolymers have a problem that the tensile modulus of elasticity is large, and the follow-up property to a board having a complicated shape is poor.
Further, also as an interlayer for laminated glass to be used for safety glass, conventional ETFE copolymers have had drawbacks that their tensile modulus of elasticity is large, they are hardly closely adhered to glass, and they are hardly processable, and the shock absorbing property at the time of breakage of the glass has not been sufficient, although the light transmittance is high and preferable.
From such a viewpoint, it is desired to lower the elastic modulus of the ETFE copolymer, and in order to lower the elastic modulus of a resin, it is generally proposed, for example, to blend an elastomer. In such a case, it is necessary to take into consideration the compatibility to the resin of the elastomer to be blended or the thermal stability at the molding temperature. Otherwise, deterioration of the light transmittance or the mechanical property such as the strength of the blend product, or an increase of the haze is likely to be brought about. In the case of the ETFE copolymer, selection of the elastomer to be blended, is difficult, and it has been difficult to solve the problems by this method.
On the other hand, it is known to lower the elastic modulus by copolymerizing a third component to the ETFE copolymer. For example, JP-B-8-5976 proposes an agricultural covering material made of a film of an ETFE copolymer wherein the ratio of the polymerized units based on TFE/the polymerized units based on ethylene is from 45/55 to 55/45 (molar ratio), and the copolymer contains from 0.1 to 10 mol % of polymerized units based on a (perfluoroalkyl)ethylene represented by CH2xe2x95x90CHCnF2n+1 (n is an integer of from 2 to 10) as a third component. However, this third component is poor in copolymerization reactivity, and the perfluoroalkyl group is of a rigid structure, and in order to obtain sufficiently low tensile modulus of elasticity, the content in the copolymer is required to be high, whereby the productivity was low with high costs.
It is an object of the present invention to provide a novel ETFE copolymer which solves the above problems.
Another object of the present invention is to provide a film having a small tensile modulus of elasticity and being excellent in flexibility, light transmittance, high strength, non-tackiness, etc., by using such a novel ETFE copolymer, and an excellent agricultural covering material, a release film and an interlayer for laminated glass, employing such a film.
The present invention provides an ETFE copolymer characterized in that the ratio of the polymerized units based on tetrafluoroethylene/the polymerized units based on ethylene, is from 35/65 to 65/35 (molar ratio), and it contains from 1 to 10 mol % of polymerized units based on an alkyl vinyl ester (provided that the carbon number of the alkyl group is from 5 to 17, and when the alkyl group contains a branched structure, the carbon number is from 9 to 17), is crystalline and has a volumetric flow rate of from 1 to 1000 mm3/sec.
A film formed of the ETFE copolymer of the present invention has a tensile modulus of elasticity as low as from 1 to 70 kg/mm2 and thus is flexible, and it is also excellent in dust-proofing property, light transmittance, strength and non-tackiness. Accordingly, it is useful for many applications. Especially, it is suitable as an agricultural covering material, a release film or an interlayer for laminated glass. The low tensile modulus of elasticity of the film of the present invention is believed to be attributable to the high copolymerization reactivity of the alkyl vinyl ester as a constituting component of the ETFE copolymer, and the crystallinity and internal plasticizing effects of the copolymer due to the alkyl group having a certain specific carbon number, in the alkyl vinyl ester.
Now, the present invention will be described in detail.
In the ETFE copolymer of the present invention, it is necessary that the ratio of the polymerized units based on tetrafluoroethylene/the polymerized units based on ethylene is from 35/65 to 65/35 (molar ratio). If the ratio of the two is not within this range, e.g. if it is smaller than 35/65, the fluorine content is small, whereby the weather resistance durability tends to be inadequate. On the other hand, if it exceeds 65/35, a haze will be formed attributable to crystalline sites, whereby the transparency tends to deteriorate. In either case, the object of the present invention can not be accomplished. A preferred range of such a ratio of the two is from 40/60 to 60/40.
The carbon number of the alkyl group in the alkyl vinyl ester as a constituting component of the ETFE copolymer of the present invention, is from 5 to 17. Especially when the alkyl group contains a branched structure, the carbon number is from 9 to 17. If the alkyl group is of a straight chain structure and has a carbon number smaller than 5, or if it contains a branched structure, and the carbon number of the alkyl group is smaller than 9, an adequately low tensile modulus of elasticity can not be obtained. On the other hand, if the carbon number of the alkyl group exceeds 17, inclusive of the case having a branched structure, it tends to be difficult to control the copolymerization composition during the polymerization, and the mechanical strength of the resulting polymer tends to be low. The above alkyl group may be one having some of its hydrogen atoms substituted by halogen atoms such as chlorine atoms or fluorine atoms.
In the present invention, the alkyl vinyl ester may be of a single type or a mixture of two or more types. Preferred specific examples of the alkyl vinyl ester to be used include, for example, vinyl caproate (the carbon number of the alkyl group is 5, which will be referred to as C5, the same applies hereinafter), vinyl caprylate (C7), vinyl caprate (C9), vinyl laurate (C11), vinyl myristate (C13), vinyl palmitate (C15) and vinyl stearate (C17).
The content of the alkyl vinyl ester in the ETFE copolymer is from 1 to 10 mol %. If the content is less than 1 mol %, an adequately low tensile modulus of elasticity can not be obtained. On the other hand, if it exceeds 10 mol %, the crystallinity of the copolymer tends to lost, whereby the mechanical strength of the resulting film tends to be low, thus leading to inconvenience, although the tensile modulus of elasticity tends to be low. Particularly preferably, the content of the alkyl vinyl ester is from 2 to 7 mol %.
The ETFE copolymer of the present invention is required to have crystallinity. Here, the crystallinity means that a peak of crystal fusion is observed by differential scanning calorimetry (DSC). Particularly preferred is one whereby the heat of crystal fusion observed at a temperature raising rate of 10xc2x0 C./min is at least 0.5 cal/g. Even if a peak of fusion is observed, if the heat of fusion is less than 0.5 cal/g, it is difficult to maintain the mechanical properties. Particularly preferably, the peak of fusion is from 0.8 to 3.5 cal/g. In the present invention, the crystallinity of the copolymer can be controlled, for example, by changing the content of the alkyl vinyl ester.
Further, the ETFE copolymer of the present invention has a volumetric flow rate of from 1 to 1000 mm3/sec. If the volumetric flow rate is smaller than 1 mm3/sec, molding of the copolymer tends to be difficult. On the other hand, if it exceeds 1000 mm3/sec, the mechanical properties tend to be inadequate. The volumetric flow rate is more preferably from 1 to 600 mm3/sec from the viewpoint of the physical properties of the film and the production efficiency. In the present invention, the volumetric flow rate is defined by a value (mm3/sec) represented by the volume of the ETFE copolymer flowing out in a unit time from a nozzle having a diameter of 1 mm and a length of 1 mm under a load of 30 kg/cm2 by means of a Kouka-type flow tester. With respect to the measuring temperature, the melting point of the copolymer varies depending upon the composition, but in the present invention, the measurement is carried out at a temperature higher by 40xc2x0 C. than the melting point.
The ETFE copolymer of the present invention can be produced by a known polymerization method such as bulk polymerization, suspension polymerization, emulsion polymerization or solution polymerization. Among them, solution polymerization is preferred, since the composition of the resulting copolymer can easily be uniformly controlled. The produced ETFE copolymer is formed into a film by a known method such as an inflation method or an extrusion molding method. With respect to the thickness of the film, if it is too thin, it is likely to break, and if it is too thick, such is inconvenient in the cutting, bonding or stretching operation, and the light transmittance tends to decrease. A preferred thickness is from 10 to 300 xcexcm, particularly preferably from 20 to 100 xcexcm. The width of the film is usually preferably within a range of from 1000 to 2000 mm from the viewpoint of the production of the film and the handling efficiency.
At the time of forming the above ETFE copolymer into a film, a colorant such as titanium oxide, zinc white, calcium carbonate, precipitated silica, carbon black, chrome yellow, phthalocyanine blue or phthalocyanine green, may be incorporated, as the case requires.
The film of an ETFE copolymer of the present invention has excellent flexibility, but preferably has a tensile modulus of elasticity of from 1 to 70 kg/mm2, particularly preferably from 3 to 60 kg/mm2. Such a film can easily be fixed to the framework of a tunnel house or a pipe house.
The tensile modulus of elasticity is measured by a method in accordance with ASTM D-1708. Namely, a microdumbbell is held at a temperature of 25xc2x0 C. in an atmosphere with a relative humidity of 50% for 40 hours and then subjected to a tensile test at a crosshead speed of 1.3 mm/min with a distance between grips of 22 mm, to obtain a stress-strain curve. The tensile modulus of elasticity is defined as a value obtained by dividing the inclination of a portion of such a stress-strain curve where the stress changes linearly to the change of strain to the yield point, i.e. the stress change (kg/mm2), by the strain. Here, the strain is one obtained by dividing the change in elongation (mm) by the initial value (mm) and is a dimensionless number.
Further, when the film of the present invention is used for an agricultural or horticultural installation such as the above house, the inside of the house is usually at a high temperature with a high humidity, and water droplets condensed inside of the ceiling or the wall are likely to deposit, and accordingly, it is preferred to treat at least the side of the film located inside of the house, with an anti-stick agent. The anti-stick agent may, for example, be of an alcohol-soluble type or a water-dispersible type, preferably one having a hydrophilic colloidal substance incorporated to a fluoropolymer such as polyfluoro acrylate, one having a surfactant incorporated to a hydrophilic polymer, or one having a surfactant and a hydrophilic colloidal substance incorporated to a hydrophilic polymer.
As the above hydrophilic colloidal substance, colloidal silica, colloidal alumina or colloidal titania, may, for example, be used. Further, the hydrophilic polymer may, for example, be a polyvinyl alcohol or a polymer having hydrophilic functional groups such as xe2x80x94SO3H, xe2x80x94COOH, xe2x80x94NH2, xe2x80x94CN or xe2x80x94(OCH2CH2)mxe2x80x94 (m is usually an integer of from 1 to 20). Further, the surfactant may be either anionic, cationic or nonionic surfactant.
The film of the present invention has a low tensile modulus of elasticity, is flexible and has a high light transmittance, whereby it can be applied to a tunnel house or a pipe house including a really large sized house for cultivation of farm crops and thus is useful as an excellent agricultural covering material.
Further, the film of the present invention is flexible and has heat resistance and non-tackiness, and thus, it is useful as an excellent release film at the time of molding a printed board. Further, the film of the present invention is flexible and has sufficient mechanical strength and high transparency, and thus, it is useful as an excellent interlayer for laminated glass, for e.g. safety glass.
Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted to such Examples. In the following, Examples 1 to 3 and 7 to 10 are Working Examples of the present invention, and Examples 4 to 6 and 11 are Comparative Examples